WEAPModel Calibration and Validation in Simulating the Impact of Irrigation Systems Change on the Ahar-Chai Basin Hydrological Response

In this study, application ofWEAP model (soil moisture method) have been investigated for simulating hydrological behavior in Ahar-Chai basin. According to the development of pressurized irrigation systems in this basin, since 2005, two models were carried out for two periods, pre-pressurized period (1998-2006) and pressurized period (2006-2013). Irrigation method in first model was surface irrigation, and in second model weresurface and pressurized irrigation. Tazekand (the basin outlet point) and Orang (upstream of the Satarkhan dam) hydrometric stations data were considered for calibration (4 year) and validation (4 year) for both models.The coefficient of determination, Nash-Sutcliffe Efficiency (NSE) and the Index of Agreement were used as statistical indices for calibration and validation of both models. The calibration of the indices for first model (1998 to 2001) in Orang station were determined 0.95, 0.82 and 0.98 respectively, and in Tazekand station werecalculated 0.96, 0.80 and 0.97, respectively. The Calibration values ​​of the indices in the second model (2006 to 2010) in Orang station were determined 0.95, 0.85 and 0.99 respectively, and in Tazekand station were determined 0.96, 0.83 and 0.98 respectively. The validation values of indices for first model (2002 to 2006) in Orang station were determined 0.98, 0.88 and 0.99, respectively, and in Tazekand station were calculated 0.96, 0.87 and 0.99, respectively. The validation values ​​of the indices in the second model (2010 to 2013) in Orang station were determined 0.96, 0.86 and 0.99, respectively, and in Tazekand station were determined 0.97, 0.78 and 0.97, respectively.